[PATCH v6 09/12] KVM: x86: Refine the matching and clearing logic for supported_xss

From: Yang Weijiang
Date: Fri Jul 16 2021 - 04:37:22 EST


From: Like Xu <like.xu@xxxxxxxxxxxxxxx>

Refine the code path of the existing clearing of supported_xss in this way:
initialize the supported_xss with the filter of KVM_SUPPORTED_XSS mask and
update its value in a bit clear manner (rather than bit setting).

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
arch/x86/kvm/vmx/vmx.c | 5 +++--
arch/x86/kvm/x86.c | 6 +++++-
2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 11d15f11ff17..3815a32166a6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7326,9 +7326,10 @@ static __init void vmx_set_cpu_caps(void)
kvm_cpu_cap_set(X86_FEATURE_UMIP);

/* CPUID 0xD.1 */
- supported_xss = 0;
- if (!cpu_has_vmx_xsaves())
+ if (!cpu_has_vmx_xsaves()) {
kvm_cpu_cap_clear(X86_FEATURE_XSAVES);
+ supported_xss = 0;
+ }

/* CPUID 0x80000001 and 0x7 (RDPID) */
if (!cpu_has_vmx_rdtscp()) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c225260c949e..2424d475a4d7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -203,6 +203,8 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
| XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
| XFEATURE_MASK_PKRU)

+#define KVM_SUPPORTED_XSS 0
+
u64 __read_mostly host_efer;
EXPORT_SYMBOL_GPL(host_efer);

@@ -10654,8 +10656,10 @@ int kvm_arch_hardware_setup(void *opaque)

rdmsrl_safe(MSR_EFER, &host_efer);

- if (boot_cpu_has(X86_FEATURE_XSAVES))
+ if (boot_cpu_has(X86_FEATURE_XSAVES)) {
rdmsrl(MSR_IA32_XSS, host_xss);
+ supported_xss = host_xss & KVM_SUPPORTED_XSS;
+ }

r = ops->hardware_setup();
if (r != 0)
--
2.21.1